Selection

• a mechanism in which physically, physiologically, environmentally and generally adapted organisms survive and reproduce
• organisms best suited in the environment survive and reproduce to pass on their allele in the net generation.
• organisms that are not suited in the environment do not survive and reproduce hence they don’t continue to exist (extinction).
• environmental factors may result in other organism best suited for surviving and other die
• Such environmental factors exert selection pressure

 

Types of selection

• Artificial Selection
• Natural Selection

 

How mutation can affect phenotype.

• gene) example ; (sickle cell / PKU )
• change in gene / DNA / base change ;
• different amino acid ;
• different polypeptide / different protein / non-functional protein ;
• (chromosome) example ; (Down’s, Turner’s syndromes)
• structural changes in chromosomes ;
• change in number of chromosomes ;
• change in sets of chromosomes / ref. polyploidy ;

 

How the environment may affect the phenotype of an organism.

• phenotypic variation results from interaction of genotype and environment
• environment may limit expression of gene(s) ;
• e.g. for size / mass / height ;
• because, food / nutrients / ion, missing / malnutrition ;
• named, nutrient / ion / mineral, missing ;
• environment may, trigger / switch on, gene ;
• ref. low temperature and change in animal colour ;
• ref. high temperature and, curled wing in Drosophila / gender in crocodiles ;
• ref. UV light and melanin production ;
• ref. wavelength of light and, flowering / germination / fruit colour ;
• other named trigger plus example ;
• environment effect usually greater on polygenes ;
• environment may induce mutation affecting phenotype ;